<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        .list{
            width: 200px;
            margin: 0;
            padding: 0;
            list-style: none;
            max-height: 30px;
            overflow: hidden;
            border: 1px solid #0b4b5a;
            transition: 0.5s;
        }

        .list:hover{
            max-height: 300px;
        }
        
        .item{
            height: 30px;
            line-height: 30px;
        }

        .item:nth-child(odd){
            background: #ddd;
        }
    </style>
</head>
<body>

<ul class="list">
    <li class="item">1</li>
    <li class="item">2</li>
    <li class="item">3</li>
    <li class="item">4</li>
    <li class="item">5</li>
</ul>

</body>
</html>